The present invention relates generally to dental appliances, and in particular to a dental appliance for introducing a filler material into a tooth cavity.
Tooth cavities are filled with various filler materials, for example amalgam. Heretofore, the dental appliances used for introducing such filler materials into the tooth cavity are of two basic types, namely one type which permits only the introduction of a quantity of the filler material into the cavity, and another type which permits only the tamping down of the introduced filler material. As every dental patient knows, this has always involved the constant exchange of one type of appliance for another as the dentist first introduces a quantity of filler material into the cavity with one appliance and then uses the other appliance to tamp it down before he can introduce an additional quantity of filler material.
The tamping appliances usually have a ball-shaped, cylindrical and conical working end which is introduced into the tooth cavity to tamp down the filler material. These appliances have not undergone any significant developments in the recent past.
The manner in which the quantities of filler material are supplied, however, has in the last few years been undergoing some changes. Conventionally, the filler material is applied by a dental aide to a small carrier which is held with one hand whereas the filler material is placed onto the carrier with the other hand. This requires quite considerable skill, and even when the filler material is correctly applied to the carrier it occurs frequently that as the carrier is being handed over to the dentist for his use it may be jogged so that the quantity of filler material placed onto it will drop off and become unusable. This evidently results in losses both of time and material.
Recognizing this problem, the prior art has attempted to provide devices to overcome it. However, these devices have all failed to take into account the particular characteristics and requirements of the filler material and therefore have not been able to fulfill their intended purpose.
To properly understand the problems involved it is necessary to keep in mind that the most widely used filler material is a silver-tin amalgam. The National Bureau of Standards, the American Dental Association and the Federation Dentaire Internationaux recommend that this amalgam be composed of 65% silver, 25% tin, 6% copper, 2% zinc, 3% mercury and traces of gold and platinum. The relatively high silver content imparts to the amalgam a considerable hardness, a low flow characteristic and a rapid setting time, whereas tin reduces expansion of the material and delays the setting. The period during which the amalgam remains plastic so that it can be worked is approximately 5-10 minutes; the time required for complete hardening is approximately 2 hours. It follows that this type of amalgam which, as mentioned above, is the most widely used today, must be introduced into an applicator appliance, ejected from the same into the tooth cavity and compacted or condensed therein, all within a period of substantially 5-10 minutes while it is still plastic.
The term condensing or compacting of the amalgam refers to the ability of the material to compact under the application of exterior pressure, leading to expulsion of air inclusions and of excess mercury. It is accepted dental practice that small quantities of amalgam are successively and rapidly applied to the tooth cavity and that they are tamped in order to first fill the retentions, corners and angles of the cavity, and to become compacted therein.
As pointed out before, the prior-art appliances which were developed for delivering quantities of amalgam into a tooth cavity do not take into account the particular characteristics of this filler material, and are therefore not usable.
It is known to provide a telescopically collapsible spiral spring which serves as a magazine for a quantity of the amalgam and also as a part of the expeller of the device. This spring has a tapering interior cross section and can be filled via a removable cap. The cross section of the inlet that is closed by the cap decreases drastically from the point where the inlet communicates with the expeller of the device to the outlet opening of the inlet nipple. Experience has shown that this prior-art device cannot be used with amalgam because the latter is a compressible medium due to the air inclusions that are present in it, so that a strong compression of the material, which leads to expulsion of excess mercury, results in a very rapid hardening of the amalgam. In the aforementioned prior-art device the material is subjected to such a strong compression and therefore tends to harden in and clog the device.
Furthermore, it is accepted dental practice to initially supply small quantities of amalgam into a tooth cavity, to be able to completely fill all crevices and angles of the cavity while obtaining good compacting, and only thereafter to supply larger quantities to fill the remainder of the cavity. The aforementioned device of the prior art operates precisely in the reverse manner, in that during the initial operation it supplies a large amount of amalgam and during successive operations it supplies smaller and smaller amounts as the amalgam begins to harden within the device.
Still another problem with this prior-art construction is the fact that its operation requires considerable skill, and that when it must be refilled with more amalgam the dentist must pass it on to an aide. In the meantime, that is while the device is cleaned out and refilled, the dentist must either interrupt the filling of the cavity or he must have a second already filled device available if he is to be able to continue the filling operation. The refilling of the device is time-consuming, especially taken in conjunction with the necessith to clean out the hardened amalgam from the previous charge, and it will be remembered that only between 5 and 10 minutes are available from the time the amalgam is prepared to the time at which it hardens and is no longer sufficiently plastic to be worked.
A further prior-art device has a tubular member which is fixedly mounted in the device and into which the body of amalgam to be dispensed must be introduced. This can be done only after the head of the device is previously removed in order to gain access to the tubular member, and this is time-consuming and of course faces the dentist with the necessity of either having to wait until the device is refilled or having to have a second identical device available that has already been previously filled so that he can continue the introduction of the amalgam into the tooth cavity. This device also has been found to be highly susceptible to malfunctions and has a relatively large working head which is disadvantageous because it requires more space than the distance of approximately 12-15 millimeters that is usually available between the rows of upper and lower teeth.
Still another prior-art device provides two plungers, one for dispensing amalgam from a magazine, and one for expelling the amalgam out of the device and into the tooth cavity. Each of the plungers must be manually operated against the force of a biasing spring. Experience has shown that this device is at best usable for dispensing of amalgam, but cannot be used for tamping the amalgam down in the tooth cavity, because for this purpose the dentist must exert with the index finger of his hand a pressure upon the front end of the device and must simultaneously maintain with his wrist the expelling plunger in forward position against the restoring force of the biasing spring. The magazine in this device is a single-use receptacle of rectangular interior cross-section which conically converges. This has the disadvantage that during the expulsion by the plunger a portion of the amalgam and of the mercury content thereof can enter behind the plunger into the free space created behind the plunger as the latter moves forwardly, so that it is subsequently difficult or entirely impossible to retract the plunger out of the container in order to be able to remove the same and replace it with a new one.
Another prior-art device has a guide channel formed with a slidable member that carries at its front end a piston, and another guide channel carrying in its interior a further slidable member that also carries a piston. One of the pistons serves to expel material from a container and the other serves to expel the material out of the device and into a tooth cavity. Both of the slidable members are biased by springs that act upon their trailing ends. One of the springs serves to maintain the piston of the expelling member within the interior of a bore until a slider is moved manually forwardly. The spring acting upon the other slideable member serves to continuously press filler material from a second channel that acts as a container into the upper hollow space of a discharge nipple. The trailing end of the expelling plunger is provided with a gear which is in engagement with a rack provided at the trailing end of the plunger that pushes material out of the reservoir.
This device is manually operated and the movement of the slider has to be carried out counter to the force of at least one spring. This not only requires the exertion of a considerable amount of force but also requires substantial skill in order to be able to rapidly fill a tooth cavity. Since the spring which acts upon the plunger that expels material from the reservoir loses its prestress as the reservoir becomes increasingly emptied of material, the amalgam portions that are expelled from the reservoir decrease successively. The original prestress of the spring acting upon the plunger for the reservoir must be relatively great, and this means that the slider must be shifted against a relatively high biasing force due to the meshing of the teeth on the gear and the rack. Moreover, this prior-art device has the further disadvantage that when the reservoir must be refilled the dentist must return the device to his aide, since the reservoir is fixedly mounted in the device and cannot be removed. He must then wait until the reservoir has been refilled or else he must have a second already filled device available for his use. This is of course time-consuming and cumbersome, especially in applications where a plurality of cavities are to be filled during a single appointment and where the working area must be repeatedly dried of saliva, etc.
Finally, another device is known from the prior art which essentially uses a double-acting pneumatic piston having a piston rod which is coupled via a bolt with a curved cam one end of which engages by means of a bifurcated member a transverse bolt of a filling pin. By alternatingly supplying air to the opposite sides of the double-acting piston the filling pin is moved up and down and pushes amalgam portions out of a reservoir that extends transversely to its movement, to expel them via a tubular nipple into the tooth cavity. In this construction, also, the reservoir piston is biased by a biasing spring which is prestressed and whose prestress continuously decreases as the reservoir empties of filler material. This means that during successive operations of the device amalgam portions of different amounts and in differentially pre-compacted condition are pushed by the reservoir piston into the path of movement of the filling pin. This device is not suitable for compacting the amalgam that has been introduced into the tooth cavity, and when the reservoir is to be refilled this is a rather time-consuming operation. A cleaning of the reservoir prior to refilling is absolutely essential, because otherwise the old residue of amalgam will harden and block the reservoir piston against movement so that it can no longer supply quantities of amalgam into the path of movement of the filling pin. Furthermore, the filling pin is not protected against pivoting in counterclockwise direction when it reaches its upper end position, so that the entire mechanism may become clogged and inoperative.